The invention relates to an arrangement for pneumatic false-twist spinning having a drafting unit which comprises devices for dividing a sliver into two partial slivers and which is followed by a pneumatic false-twisting device.
In the case of a known arrangement of the initially mentioned type (German Patent Document DE-A 38 42 120 and corresponding U.S. Pat. No. 4,942,731 to Morihashi et al.), a drivable biconical wheel is arranged inside the drafting unit between the intake roller pair and the next roller pair, which, in the manner of a separating wedge, divides the entering sliver into two partial slivers. These slivers then travel separately through the apron guide and the delivery roller pair as well as through separate air nozzles of the false-twisting device. They are subsequently guided together in front of a common withdrawal device and, while they are disposed side-by-side, are wound onto a spool as a double yarn.
It is also known (German Patent Document DE-A 39 01 791) to divide the sliver fed by a drafting unit into two partial slivers which are each fed to a ring spindle. In the case of this construction, it is provided that the sliver is not divided into the two partial slivers until it has passed through the drafting unit, that is, at the pair of delivery rollers of the drafting unit. For this purpose, one of the two delivery rollers is constructed as a suction roller which is provided with two suction slots which diverge from the area of the nip line. These suction slots each taper in the yarn travelling direction in order to be provided with a certain bundling of the two partial slivers.
It is an object of the invention to improve an arrangement of the initially mentioned type in such a manner that a larger quantity of edge fibers are spread away which subsequently can be utilized as wind-around fibers and which provide the yarn with a more uniform appearance and/or an increased strength.
This object is achieved according to preferred embodiments of the invention in that a roller of the pair of delivery rollers of the drafting unit is constructed as a suction roller which forms two suction zones which divide the sliver behind the nip line into the partial slivers and spread edge fibers away from the partial slivers.
The invention is based on the recognition that, when the division into the two partial slivers does not start before the area of the nip line of the pair of delivery rollers, it is possible to spread away a larger quantity of edge fibers. However, for this purpose, care must be taken that the partial slivers are not bundled as in the case of the construction according to the German Patent Document DE-A 39 01 791 but that, on the contrary, edge fibers are intentionally spread away.
In order to carry out an intentional spreading-away of edge fibers, it is provided in a further development of the invention that the suction roller provided with a perforation has a suction insert which has two suction zones moving away from one another starting from the area of the nip line in the travelling direction of the yarn, the effective width of these suction zones increasing in the travelling direction of the yarn. It is particularly advantageous in this case for the two suction zones to each start as a suction slot which are in each case continued by two slots extending in parallel to one another. The slots, which each extend in parallel to one another, will then be situated next to the partial sliver so that edge fibers are spread away toward both sides and are held in this spread-away position.
In a further development of the invention, it is provided that a pressure roller is assigned to the suction roller and is arranged in the area of the ends of the suction zones. As a result, it is achieved that the false twist, which originates from the false-twisting device, is stopped in the area of the pressure roller so that it does not impair the spreading-away of edge fibers.
In a further development of the invention, it is provided that the false-twisting device for each of the partial slivers has at least one air nozzle. In a first embodiment, it is then provided that the air nozzles are followed by separate wind-up devices for each of the partial slivers. The partial slivers are therefore spun into respective separate yarns which are wound onto separate spools.
In a modified embodiment, it is provided that the air nozzles are followed by devices for the guiding-together of the spun partial slivers and by a common wind-up device. The spun partial slivers are then wound onto a common spool as a double yarn. In this case, it is expediently provided that the two partial slivers are not spun completely but are only prestrengthened. The spool package, which receives the double yarn, will then be fed to a twisting machine so that the final strength of the yarn is obtained by means of a twisting. In the case of this embodiment, it is advantageous for the devices for the guiding-together to form travelling paths of a different length for the two spun partial slivers. As a result, it is achieved that the two partial slivers with respect to their length are guided together again in an offset manner so that a doubling effect is obtained which compensates possible inaccuracies as a result of the sliver division.
In another embodiment of the invention, a false-twisting device is provided which both partial slivers have in common and which comprises at least one air nozzle. In this embodiment, a common yarn is then again spun from the two partial slivers. In this case, the division of the slivers results in the advantage that a significantly higher number of edge fibers were spread so that an improved winding-around and therefore a particularly firm yarn is achieved.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.